Electret Microphone

How to use a electret microphone with a balanced phantom powered input.

We use the Primo EM172, a 12€ high quality electret microphone. The circuit presented here can be use to build a monophonic streambox, or with two of them a binaural head.

The presented circuit power the electret microphone with a bias voltage determined by the value of a zener diode. Usualy 5 volts is enought, but I find out 12v works better with the Primo EM172. It use the +48v from the phantom power, and output a balanced signal. This way, an extended length of cable can be used with very little background noise.

The circuit can be assembled on test board. Butif you want to print it, you can find the eagle files here.

Here are a few complete circuits.

It has been working outside for years, and is proven to be reliable. However, if left outside, coating the circuit is a good precaution, otherwise the humidity from the air with the +48v will disolve your trace, as it happend to me: